Usually these things are decided by project management concerns, IE, the decorator comes in after everyone else has finished. If you're doing it all yourself and looking for some ideal order, it would depend a lot on your experience and comfort with each skill.
I would feel confident installing a floor without damaging walls. I would also feel protecting a floor is easy, and protecting walls is a huge pain. So the whole "damage" train of thought doesn't do much for me here. Either way is fine.
I would do the floor first, cover it, do the skirting, paint the new skirting (you didn't mention that) then do the wallpaper.
In my personal hierarchy of things I can mess up, and what I can do to prevent it, getting paint on the wallpaper is top of the list, and taping the wallpaper carefully, then removing the tape without damaging my new paint, would be the thing I want to avoid most. OTOH getting some wallpaper glue on the new skirting is no big deal. I'm going to clean up anyway.
And take Freeman's advice, don't swing long boards around. :)